Traffic control and Quality of Service

1
Traffic control and Quality of Service

• Reading Chapter 18

2
Some basic concepts

• Traffic policing
• Incompliant packets dropped
• Traffic shaping
• Incompliant packets held till satisfied
• Queueing discipline
• Packet departure order (time)
• Classes
• Packet holders
• Filters
• Packet classifiers

3
Traffic control in Linux kernel
...
..
p8022_rcv
arp_rcv
ip_rcv
ip_queue_xmit
arp_send
Layer 3
ETH_P_802_2
dev.c
br_input.c
dev.c
...
net_rx_action
handle_bridge
dev_queue_xmit
CONFIG_BRIDGE
dev-gtqdisc-gtenqueue
do_softirq
Scheduler
eth0
eth1
CPU1
CPU2
dev.c
net_tx_action
qdisc_run
softnet_datacpun.input_pkt_queue
Data-link layer (OSI-Layer 12)
dev.c
netif_rx
qdisc_restart
Scheduler
eth_type_trans()
driver.c
dev-gtqdisc-gtdequeue
dev_alloc_skb()
driver.c
net_interrupt
dev-gthard_start_xmit
4
Traffic control
dequeue
enqueue
One specific queueing discipline
5
Basic queue discipline interface

• enqueue()
• Put a packet into queue
• dequeue()
• Get a packet from the queue
• drop()
• Remove a packet
• requeue(), reset(), init(), destroy(), change(),
  dump()

6
struct Qdisc
Struct Qdisc int (enqueue)() struct
sk_buff (dequeue)() struct
Qdisc_ops ops struct Qdisc next struct
sk_buff_head q struct net_device dev
7
Adding a discipline into kernel

• pktsched_init()
• Used when a discipline is compiled permanently
  into kernel
• Initializing RT-NETLINK interface
• Calling register_qdisc() function
• register_qdisc()
• Called by pktsched_init() or init_module()
• Inserting discipline into the list
• Allocating operations (functions)

8
Filters

• classify()
• init()
• destroy()
• delete()

9
Implementing a discipline

• Concepts of token bucket filter
• Rate R
• Depth B
• Functions
• tbf_init()
• tbf_enqueue()
• tbf_dequeue()