Unlike the Internet 2 Abilene Network, the Internet is actually a series of exchange points interconnecting private networks and not a network in its own right.[5] Hence the Internet's core is owned and managed by a number of different Network Service Providers, not a single entity. Its behavior is much more stochastic or unpredictable. Therefore, research continues on QoS procedures that are deployable in large, diverse networks.
There are two principal approaches to QoS in modern packet-switched networks, a parameterized system based on an exchange of application requirements with the network, and a prioritized system where each packet identifies a desired service level to the network. On the Internet, Integrated services ("IntServ") implements the parameterized approach. In this model, applications use the Resource Reservation Protocol (RSVP) to request and reserve resources through a network.
Differentiated services ("DiffServ") implements the prioritized model. DiffServ marks packets according to the type of service they need. In response to these markings, routers and switches use various queueing strategies to tailor performance to requirements. (At the IP layer, differentiated services code point (DSCP) markings use the first 6 bits in the TOS field of the IP packet header. At the MAC layer, VLAN IEEE 802.1q and IEEE 802.1p can be used to carry essentially the same information.) Diffserv internally assumes over-provisioning within its delay-sensitive Expedited Forwarding, class. This assumption is not always justifiable in the Internet, making it a contributing factor to the lack of DiffServ implementations in networks that transit the Internet.
Cisco IOS NetFlow and the Cisco Class Based QoS (CBQoS) Management Information Base (MIB) can both be leveraged within a Cisco network device to obtain visibility into QoS policies and their effectiveness on network traffic. [6]
Non-IP protocols, especially those intended for voice transmission, such as ATM or GSM, have already implemented QoS in the core protocol and don't need additional procedures to achieve it.
There are two principal approaches to QoS in modern packet-switched networks, a parameterized system based on an exchange of application requirements with the network, and a prioritized system where each packet identifies a desired service level to the network. On the Internet, Integrated services ("IntServ") implements the parameterized approach. In this model, applications use the Resource Reservation Protocol (RSVP) to request and reserve resources through a network.
Differentiated services ("DiffServ") implements the prioritized model. DiffServ marks packets according to the type of service they need. In response to these markings, routers and switches use various queueing strategies to tailor performance to requirements. (At the IP layer, differentiated services code point (DSCP) markings use the first 6 bits in the TOS field of the IP packet header. At the MAC layer, VLAN IEEE 802.1q and IEEE 802.1p can be used to carry essentially the same information.) Diffserv internally assumes over-provisioning within its delay-sensitive Expedited Forwarding, class. This assumption is not always justifiable in the Internet, making it a contributing factor to the lack of DiffServ implementations in networks that transit the Internet.
Cisco IOS NetFlow and the Cisco Class Based QoS (CBQoS) Management Information Base (MIB) can both be leveraged within a Cisco network device to obtain visibility into QoS policies and their effectiveness on network traffic. [6]
Non-IP protocols, especially those intended for voice transmission, such as ATM or GSM, have already implemented QoS in the core protocol and don't need additional procedures to achieve it.
No comments:
Post a Comment