3750 QoS - egress interface

Please guide me to understand the 3750 QoS mechanism.
Q1) DOC say "priority-queue out" is ignore shape and share command. is it meaning always give priority to cos=5(or dscp=ef) traffic regardless the shape command?
Q2) I want to give 10% guaranteed bandwidth to voice traffic. what's best command in the 3750 egress interface? shape only or combine with priority-queue?
Q3) Any doc explained the output for the command "show mls qos interface f1/0/1 statistics"? the meaning of the each field.
Thanks in advance,

Hi,
1. That is correct. The expedite queue is a priority queue, and it is serviced until empty before the other queues are serviced. This has the potential to hog all the bandwidth on an interface....
2. I would use the priorty-queue command as it will give the best jitter and latency characteristics for your voice traffic. If you want to limit this bandwidth, you should do it via policing on ingress interfaces.
3. Check out this link:
http://www.cisco.com/en/US/products/hw/switches/ps5023/products_command_reference_chapter09186a00805023be.html#wp1947019
Hope that helps - pls rate the post if it does.
Regards,
Paresh

Similar Messages

3750 qos - buffer size

I am putting together a VOIP qos config for a number of different switch types on of which is the 3750. We have a load of these switches an although the SRR method is different to me I think I have a handle on it.
The software config guides make numerous mention of configuring the queue sizes and weights etc in terms of buffer space percentage.
I believe that the amount of space available for egress and ingress buffers is fixed so I have a simple question.
What is the size of the total available buffer space either in bytes or number of packets ?
I cant find this anywhere. Seems to me that trying to allocate buffer space and weights without this info is more or less guessing.
I have the software config guide which is quite good but seems to leave out this kind of info, can anyone suggest a more complete document which may help ?
Many Thanks
Shaun

two things...first things first:
1) see if AutoQoS (introduced in 12.2(15)T) will work for you to create a baseline QoS requirement...this may allieviate your need to crunch so many numbers/scenarios before you actually know what QoS your network requires.
2) the queues can be shared by percentage or shaped by bandwidth.
see the following links for 3750 QoS sharing & shaping:
http://www.cisco.com/en/US/products/hw/switches/ps5023/products_white_paper09186a00801b096a.shtml#wp41099
see the following link for more info on 3750 QoS:
http://www.cisco.com/en/US/netsol/ns577/networking_solutions_white_paper09186a00801eb831.shtml

QOS: egress police command not supported in non-leaf classes

Hello,
I have issue with egress policers on EFP (Service instance).
When configure two egress policers on EFPs (on one physical interface), I received a message:
ME-3600X(config-if-srv)#service-policy output VLAN-50M
QOS: egress police command not supported in non-leaf classes
QoS: Policy attachment failed for policymap VLAN-50M
The configuration looks easy:
policy-map VLAN-50M
class VLAN
police cir 50000000
exceed-action drop
class-map match-all VLAN
match protocol ip
interface GigabitEthernet0/11
description TEST
switchport trunk allowed vlan none
switchport mode trunk
mtu 1998
load-interval 30
service instance 199 ethernet
encapsulation dot1q 199
rewrite ingress tag pop 1 symmetric
service-policy output VLAN-50M
xconnect 82.119.245.231 3291 encapsulation mpls
service instance 500 ethernet
description L2MNG-SWITCHE
encapsulation dot1q 500
rewrite ingress tag pop 1 symmetric
bridge-domain 500
I tried to attach the same policy-map to Service Instance 500, with the messages above mentioned.
I am not sure if this is correct behaviour, and what means term "non-leaf class".
IOS version is 15.2(4)S2 with AdvancedMetroIPAccess.
Best regards,
Josef

Platform supports three level hierarchy - Port, VLAN and Class.
Class is the leaf level.
Queuing is done only at the leaf level.
You need to attach your policy to the port level policy so that it can be a two level policy.
Three Level Class-default Policy Example:
policy-map leaf
class class-default
queue-limit xxxxx bytes
policy-map logical
class class-default
service-policy leaf
policy-map root
class class-default
service-policy logical
Invalid Queue-Limit Policy Configuration Example:
This case "class-default" is being considered as the port level.
Following QOS policy configuration failed because the configuration check assumes user is trying to apply the queue-limit at the vlan level which is not supported.
policy-map child-1
class class-default
queue-limit 256 packets
policy-map VLAN-OUT
class class-default <<< Class default is being assumed at the port level , Child policy at the second level
shape average 5000000
service-policy child-1
interface GigabitEthernet0/5
switchport trunk allowed vlan none
switchport mode trunk
service instance 2 ethernet
encapsulation dot1q 60
rewrite ingress tag pop 1 symmetric
bridge-domain 60
3600-HL-2-N(config)#interface GigabitEthernet0/5
3600-HL-2-N(config-if-srv)#service-policy output VLAN-OUT
QOS: queue-limit command not supported in non-leaf classes
QoS: Policy attachment failed for policymap VLAN-OUT
*Feb 13 09:55:28.700: %QOSMGR-3-QLIMIT_LEVEL_ERROR: Qlimit command not supported in non-leaf classes

ASA 5505 initial build - Failed to locate egress interface (Please help :-) )

Hi, I have just purchased a ASA 5505 and have completed the initial setup via the wizard. I am currently unable to access services on the outside of the ASA.
The error: 'Failed to locate egress interface for UDP from inside'.... appears when ever my DNS server attempts a lookup.
I have configured this several times from scratch using the wizard and I am unable to figure out the issue with the NAT / Routing config.
If I run the packet tracer I get the error: "(no-route) no route to host", however I do have a default route configured so I suspect it maybe my NAT configuration.
Overview, 192.168.10.0/24 inside the ASA, 192.168.1.0/24 outside the ASA, 192.168.1.1 is the gateway to the internet. I ideally want the ASA to use PAT to mask the 192.168.10.0/24 network behind the ASAs 192.168.1.0/24 network address but still allow clients to gain internet access.
Full config follows, screen shots attached, any help would be very gratefully received.
Result of the command: "sh run"
: Saved
ASA Version 9.0(1)
hostname firewall
enable password (REMOVED) encrypted
passwd (REMOVED) encrypted
names
interface Ethernet0/0
switchport access vlan 2
interface Ethernet0/1
interface Ethernet0/2
interface Ethernet0/3
interface Ethernet0/4
interface Ethernet0/5
interface Ethernet0/6
interface Ethernet0/7
interface Vlan1
nameif inside
security-level 100
ip address 192.168.10.1 255.255.255.0
interface Vlan2
nameif outside
security-level 0
ip address 192.168.1.254 255.255.255.0
interface Vlan5
no nameif
security-level 50
ip address dhcp
ftp mode passive
object network obj_any
subnet 0.0.0.0 0.0.0.0
object network Server1
host 192.168.10.10
object network GoogleDNS1
host 8.8.8.8
description Google DNS Server
object network GoogleDNS2
host 8.8.4.4
description Google DNS Server
object network 192.168.10.x
subnet 192.168.10.0 255.255.255.0
object network InternetRouter
host 192.168.1.1
object-group network DM_INLINE_NETWORK_1
network-object object GoogleDNS1
network-object object GoogleDNS2
object-group service DM_INLINE_TCP_1 tcp
port-object eq www
port-object eq https
access-list inside_access_in remark External DNS Lookups
access-list inside_access_in extended permit udp object Server1 object-group DM_INLINE_NETWORK_1 eq domain
access-list inside_access_in extended permit tcp 192.168.10.0 255.255.255.0 any object-group DM_INLINE_TCP_1
access-list inside_access_in extended deny ip any any
pager lines 24
logging enable
logging asdm informational
mtu inside 1500
mtu outside 1500
icmp unreachable rate-limit 1 burst-size 1
no asdm history enable
arp timeout 14400
no arp permit-nonconnected
nat (inside,outside) source dynamic any interface
object network obj_any
nat (inside,outside) dynamic interface
access-group inside_access_in in interface inside
route outside 0.0.0.0 255.255.255.255 192.168.1.1 1
timeout xlate 3:00:00
timeout pat-xlate 0:00:30
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02
timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 mgcp-pat 0:05:00
timeout sip 0:30:00 sip_media 0:02:00 sip-invite 0:03:00 sip-disconnect 0:02:00
timeout sip-provisional-media 0:02:00 uauth 0:05:00 absolute
timeout tcp-proxy-reassembly 0:01:00
timeout floating-conn 0:00:00
dynamic-access-policy-record DfltAccessPolicy
user-identity default-domain LOCAL
http server enable
http 192.168.1.0 255.255.255.0 inside
http 192.168.10.0 255.255.255.0 inside
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart warmstart
crypto ipsec security-association pmtu-aging infinite
crypto ca trustpool policy
telnet timeout 5
ssh timeout 5
ssh version 2
console timeout 0
dhcpd auto_config outside
threat-detection basic-threat
threat-detection statistics access-list
no threat-detection statistics tcp-intercept
prompt hostname context
no call-home reporting anonymous
Cryptochecksum:(REMOVED)
: end

Just to want to be sure, can you post output from show int ip brie and show route? And try to remove your ACL for testing purpose or at least don't applied it anywhere yet.
Once done, try do another packet-tracer to 8.8.8.8 using icmp packet instead of UDP paste the whole the output here. Before doing this, add icmp any any outside command on the ASA.
I know this should have anything to do with your issue, because if ACL is the issue then you will see output being denied by ACL on the packet tracer output. Let us know the results.

ASA9.1 how to use route-lookup instead of "NAT-lookup" for egress interface on non-identity NAT

Hi,
I have an ASA firewall with three interfaces, inside, outside and Link.
I have a situation where I need the ASA to perform the following nat rules:
from "Inside" to "Link" - any source to destination 192.168.51.0/24 - translate source to 10.0.0.19
from "inside" to "outside" - any source to any destination - translate source to "interface" (internet navigation)
from "inside" to "outside" any source to 192.168.51.0/24 - translete source to 10.0.0.17
This is what I am trying to get working:
nat (any,TEF) source dynamic any 130.130.0.19_nat destination static obj_192.168.51.0 obj_192.168.51.0
nat (any,outside) source dynamic any 130.130.0.17_nat destination static obj_192.168.51.0 obj_192.168.51.0
The problem is that the "outside" route to 192.168.51.0 is an alternative route over a VPN tunnel. I'm using sla monitor, so when the "Link" interface is out, the route table changes the network 192.168.51.0/24 to be reachable over the outside interface. but ASA is using the NAT rule to perform "egress interface lookup" instead of route-lookup.
I know about the command route-lookup on the NAT configuration, but I need to translate the source address and when I try to use the route-lookup command I get an error message:
ERROR: Option route-lookup is only allowed for static identity case
Anybody has some suggestion?
Thanks

Hi Julio,
Thank you for the reply.
It didn't work either.
Here are the options I get when I use the specific interfaces (using "source dynamic"):
configure mode commands/options:
description Specify NAT rule description
inactive Disable a NAT rule
net-to-net Net to net mapping of IPv4 to IPv6
service NAT service parameters
If I try to use source static:
nat (inside,TEF) source static inside_nat 130.130.0.19_nat destination static obj_192.168.51.0 obj_192.168.51.0 route-lookup
ERROR: Option route-lookup is only allowed for static identity case

Traceroute issue - CE router replys 2 hops on ingress & egress interfaces

Hi Guys,
Please help to explain the following traceroute issue :
I have 2 Cisco Routers R1 & R2 on two sites, both of them are connecting to Telco MPLS/VPN cloud. When I do traceroute from R1 to R2, I found the first 2 hops reflect the ingress and egress interfaces on the same CE router, which is connecting to R1. Please see following details:
Traceroute path (on R1, do traceroute R2's loopback address):
R1 -- CE1 -- PE1 -- PE2 -- CE2 -- R2
Tracing output:
1. CE1_ingress_int
2. CE1_egress_int
3. CE2_ingress_int
4. R2_ingress_int
FYI: the /30 link route between CE1 & PE1 is not advertised to R1. not sure if this affects or not.
I have no access to to the Telco CEs & PEs , I assume it might be related to CE1's MPLS traceroute configuration. Or it might be related to the ttl propagation between the IP & MPLS domain?
Your help is highly appreciated!
Thanks and best regards
Jerry

It is hard to figure out what the issue is without having a look at CE1.
Are you certain that the second entry you are seeing is CE1 egress interface IP address and not PE1 ingress interface IP address?
The fact that the CE-PE /30 subnet is not known by R1 has nothing to do with the behavior you are seeing.
Hope this helps,

3750 qos on routed interface

I have 2 3750G-24 as the core of my voice/data network. I have 2 vlans (voice,data) and it seems like when I cross the routed interfaces (virtual vlanX interfaces) I lose my qos tagging. I have tried route-maps and policy maps but they are not working (the policy maps are not supported on virtual interfaces)
Anyone with a solution?? I have searched cisco.com and unless i am blind, have not found what I am looking for.

Here is the edge switchport config-
End user port-----
interface FastEthernet0/1
switchport access vlan 50
switchport trunk encapsulation dot1q
switchport trunk native vlan 50
switchport mode trunk
switchport voice vlan 10
mls qos trust device cisco-phone
mls qos trust cos
auto qos voip cisco-phone
wrr-queue bandwidth 20 1 80 1
wrr-queue min-reserve 1 5
wrr-queue min-reserve 2 6
wrr-queue min-reserve 3 7
wrr-queue min-reserve 4 8
wrr-queue cos-map 1 0 1 2 4
wrr-queue cos-map 3 3 6 7
wrr-queue cos-map 4 5
priority-queue out
spanning-tree portfast
Gigabit uplink port------------
interface GigabitEthernet0/1
switchport trunk encapsulation dot1q
switchport mode trunk
mls qos trust cos
auto qos voip trust
wrr-queue bandwidth 20 1 80 1
wrr-queue queue-limit 80 1 20 1
wrr-queue cos-map 1 0 1 2 4
wrr-queue cos-map 3 3 6 7
wrr-queue cos-map 4 5
priority-queue out
end
Here is the core switch-
interface GigabitEthernet1/0/24
switchport trunk encapsulation dot1q
switchport mode trunk
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
mls qos trust cos
no mdix auto
auto qos voip trust
end
Core Vlan Interfaces----
interface Vlan1
no ip address
interface Vlan2
description Data Vlan
ip address 10.199.0.29 255.255.252.0
interface Vlan10
description Voice Vlan
ip address 10.199.10.1 255.255.255.0
All of the qos settings are a result of using Auto QoS

Cat. 3750 QoS Queue statistics

Hi all:
Does anyone know a way to see input and output queue statistics like occupation, number of frames discarded due to threshold reached etc ... on a Cat 3750
May be there exists a MIB...
Best regs.

the command "show mls qos interface" should help.
check out the following link for the command reference :
http://www.cisco.com/en/US/products/hw/switches/ps5023/products_command_reference_chapter09186a008017f8ed.html#2418190

3560/3750 QoS "cheat" sheet?

Hi folks
I remember not that very long ago I saw a document that was depicting the QoS order of operation for both ingress and egress data flows on the Cisco 3560/3750 series.
However, I'm at a loss right now as I cannot find it, apparently I didnt bookmark it. :-/
I was hoping that one of you guys might happen to know which one I'm talking about and point me in the right direction. I know it's not much to go on...
Thanks in advance!

Hey Rajeevsh
Thank you for the reply, but it was not the one I was looking for. I've finally manged to find it. It was this one I was looking for:
http://rizzitech.blogspot.com/2010/08/qos-on-cisco-3560-diagram.html
Have a nice day :)

Help: How to choose egress interface by the internal source IP in ASA5520?

Hi there,
I'm using ASA 5520: ASA ver 8.4(4)1, ASDM ver 6.4(9), firewall mode: Routed.
There are 2 WAN Interfaces for this ASA: Port 0/3 named 100M; Port 0/0 named Outside.
One LAN interface is Port 0/1 (10.1.0.0/16) There are 2 groups of users, which can be diffentiate by their IP addresses.
UserGroup A: 10.1.6.0/24; UserGroup B is all other LAN users, 10.1.0.0/16, except 10.1.6.0/24.
I'd like to route the Internet traffic as below:
When A accesses Internet, traffic goes thru Port 0/3.
When B accesses Internet, traffic goes thru Port 0/1.
I can't set static-route by checking their source IP, I can't set policy based routing either.
How can this be achieved in my ASA5520?
Thanks,
Tony

Hi,
I guess you need to use a separate router to do the PBR on the basis of the public NAT IP address (and then choose the correct gateway) of the users or build something on the LAN side in the sameway
I guess you could also separate the users on different LAN networks and change the ASA to run in multiple context mode and create different firewall context for both LAN networks (I think every ASA has a license that permits 2 context (admin context isnt counted into this), you can check it with "show version" command). Then again this option would eliminate the use of VPN. (Though L2L VPN are supposedly coming available in multiple context mode later)
Something tells me though that the second option would simply mean too much work or if you are using VPN on the ASA it would mean you would need separate VPN device.
- Jouni

CAT 3750 QOS+ Polycom Video Conferencing + Voice

I am wondering has anyone out there has a good example or how to Tune DiffServ parameter in IOS 12.2(25)SEA that can get an Optimal response on a T1 WAN Link.
1)Voice: Expedited & rate limited to Not more than 350Kbps
2)Video: about 400Kbps
3)Telnet & other mission critical Apps limited to 200Kbps
4)FTP, HTTP: Ratelimited to 500K
5) Rest of Bandwidth for other traffic.
Any help is appreciated.

Please refer to the QoS configuration guide for tuning the DiffServ parameter.
http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_guide_chapter09186a00803947f0.html

CoPP policies on Nexus 3k/5k

Hi. Is there any documentation on defined tasks of certain CoPP policies. While most are guessable then there are some that I have no clue about.
For example class-map copp-s-selfIp ... if I had traffic matched by that policy exceeding the defined pps then I would have no clue what traffic is actually flooding the control plane.
Is there a source for that kind of information?
thanks!

Those are different things.
Policy type qos --> Function: Define traffic classification rules -->attached under System qos and Ingress Interface
policy type queuing -->Function: Strict Priority queue & Deficit Weight Round Robin --> attached under: System qos & Egress Interface & Ingress Interface*
network-qos -->Function: System class type(drop or no-drop) & MTU per class of service & Buffer size &Marking --> Attached under:System qos

Router Interface (7304 NSE100) QoS Input Scheduling

Guys,
I had great feedback on the Switch input scheduling question last week. Many thx to all online (and my colleagues at work) :)
If you can apply input scheduling on a switch port, ie the SP or default queues, can you apply input scheduling on a router interface?
switch
input-q----------PFC----------output-q
router
input-int---------cef-or-rp----------output-int
At the moment, most QoS for a router is done (in my expreience) on outbound scheduling, ie setting a CBWFQ bandwidth or priority and setting this policy-map outbound on the router egress interface
Should we be doing it inbound for traffic coming into a router interface before the packet gets cef switched (or sent to the RP for process or fast switching)?
So if two packets come into the router interface at the same time, based on a DSCP value, we should schedule a voice packet to be processed by CEF switching (or the RP) before an email packet?
I am just applying the switch methodology that I learned about last week to a router device. I know all routers have different archetectures, so will probably be spefific to a platform. I am using NSE100s (PXF based) on a 7304 platform.
Kindest regards,
Ken

Just to add i picked this from some site
GSR:
Engine 0: (Quad STM-1 POS/ATM, single STM-4 POS/ATM and others)
Engine 1: (single GEth, 8 FEth, DPT 2XSTM-4)
Engine 0 and 1 support CAR in sw; MDRR: in Engine 0 in sw
Engine 2: STM-16, Enhanced Quad OC-12/STM-4 Packet-over-SONET/SDH - 4 ports, MPLS-capable -, 8 and 16 STM-1, 3 GEth, Enhanced OC-48/STM-16 Packet-over-SONET/SDH.
no support of CAR, PIRC in hw instead; WRED in hw; MDRR in hw
(See also Quad OC-12/STM-4; Rel. Notes 12.0 S )
Engine 4: speed greater than 2.5 Gbps,
CAR, WRED, MDRR in hw
Note: no class-based shaping on GSR
But it supports DTS
http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/products_feature_guide09186a00800811e5.html
Tuf luck but hope this helps

QoS for App-V

Hello,
I'm currently configuring new 3750X switches.
I must implement QoS on the stack. The QoS must be the following:
VOIP Class (50%)
App-V Class (40%)
Movie Class (10%)
How I can do this (in particular for AppV)? I do the following for the moment:
class-map match-any VOIP
match protocol voice
match dscp ef
match protocol sip
match protocol skype
match protocol rtp audio
match protocol rtp video
exit
class-map AppV
exit
class-map Movie
match protocol rtp video
exit
policy-map BandwidthTraffic
class VOIP
priority percent 50
set dscp ef
class AppV
bandwidth remaining percent 40
class Movie
bandwidth remaining percent 10
interface Gig1/0/3
ip nbar protocol-discovery
service-policy input BandwidthTraffic
Anyone can says me if it's correct or not? And why?
Thank you for your help.
Florent

Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
It appears you've some router QoS. 3750X QoS is quite different for egress as you're limited to working with four egress queues. I don't recall 3750X supporting NBAR.
Suggest you read the configuration guide's chapter on QoS, for you 3750X IOS version, and then post questions as necessary. (My concern is, 3750X QoS is so different, it wouldn't be helpful to suggest a QoS configuration until you had a basic understanding of the 3750 QoS architecture and features.)

Best QOS Practice for a congested Uplink Port?

I have an MPLS uplink port to a carrier that carries both voice and data.
For example, Customer 3750 Switch 100MB Uplink--->100MB Uplink Carrier Router---Carrier Router 6MB MLPP Voice/Data MPLS Uplink with QOS configured for Voice subnet on carrier side too.
The port occasionally suffers from overutilizition and spikes to the full 6MB
I have a centralized CUCM that has phones that occasionally reset due to TCP 2000 timeouts (usually during the period of high utilization)
So that I can avoid most phone resets during high utilization I have prioritized all voice traffic (signalling and RTP streams) to EF
My question: What is best practice configuration for a congested uplink port? I'm going to assume the answer is it depends (the all great technical answer )
Here are my thoughts on how to configure the 3750 uplink port so far:
apply mls qos trust dscp
apply priority-queue out
(Here's where I'm looking for help)
apply some sort of policing or bandwidth statement on the interface to protect the voice traffic: What are the recommendations and what would those configurations look like?
I would apply these these configurations to the uplink ports at the edge site as well as the central site.
Any thoughts as to the best way to accomplish this?

Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
You want to prioritize VoIP traffic at congestion points, which for you, looks to be whenever your LAN bandwidth hits your 6 Mbps WAN.
If the carrier takes your 100 Mbps, and doesn't just generally police all traffic to 6 Mbps, but instead has different priority queues for the 6 Mbps, all you should need to do, is insure you traffic is correctly processed by your WAN vendor. This, though, might require marking your traffic for the WAN provider.
If you carrier first polices all your traffic at 6 Mbps (many do), then you need to shape the traffic (with you own prioritization) before the provider "sees" it. If you need to "shape" on the 3750, there's a command to limit a port's bandwidth utilization, as a percentage. However it's not exact, so you may need to "shape" slower than 6 Mbps to insure 6 Mbps won't be exceeded. (BTW, for 6 Mbps, if you need to do QoS, you would be better off with an ISR.)
You also mention 6 MLPPP, but it's unlclear what your device is for that.
How to configure 3750 QoS is involved. Basically when you enable QoS, each port has four dedicated egress queues. By default, different traffic markings go into one of the four queues, each queue has same share of the bandwidth, and almost same share of the buffers. The PQ command you noted, enables the first queue to always transmit its packets first. Normally, you'll want to do that for VoIP bearer packets, which you've (insured are) directed to that queue. You also want to insure that VoIP signally packets are not likley to be dropped and, more or less, are forwarded quickly.
Cisco has multiple papers on QoS configurations, including papers for 3750s, so instead of my trying to present that, the above is intended as an overview. Feel free to post additional questions, the more specific, the more likely you'll get an answer.

3750 QoS - egress interface

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