Network2/Dynamics: Difference between revisions

Latest revision as of 20:14, 29 August 2010

Prerequisite concepts: bandwidth, latency, jitter, availability, model, unicast, multicast, broadcast, network stack

First, some baseline analysis:

Suppose we have a wireless link with capacity C.
Suppose we have N nodes.
Suppose each node n wants to maintain f(n) connections.
If f(n) = 1 then we could allocate up to C/N per connection.
If f(n) = N then we could allocate up to C/N^2 per connection.

Instructive values: C=30 Mbps, N=40, f(n)=N ==> 19 Kbps / conn. Conclusion: beware O(N^2) behavior.

Several important numbers that we need to predict and to measure include bandwidth and latency figures:

tx == transmit, rx == receive, btx == broadcast

btx/tx/rx - ICMPv6+IPv6+phys           - router discovery (RD)
btx/rx    - ICMPv6+IPv6+phys           - duplicate address detection (DAD)
tx/rx     - ICMPv6+IPv6+phys           - NS neighbor discovery (ND)
tx/rx     - UDP+IPv6+phys              - DNS query
tx/rx     - JSON+SSH+TCP+IPv6+phys     - DNS update

where "phys" describes the equations' dependence on the "physical" layer's 
frame overhead and MTU

notable "phys" layers:

Ethernet           -- ad-hoc wifi, infra wifi, 802.11s mesh, switch, hub
TLS+UDP+IPv4       -- openvpn
L2TP+IPsec+IPv4    -- raccoon, isakmpd, openswan, etc.
UDP+IPv4           -- teredo

Baseline overheads:

Ethernet: 18

IPv4: 20 + options
IPv6: 40 + options

ICMPv6: 4
ICMPv6 RA: 16 + prefix+{32} + mtu?{8}

UDP: 4
TCP: 20 + options?

TLS: 5 + mac?{16,20,32} + pad?{4,8,16}
D-Bus: 12 + type-array
XMPP MUC: 50 + jids

@@ Line 1: / Line 1: @@
 {{Network2 header}}
 Prerequisite concepts: [[Network2/Concept/Bandwidth|bandwidth]], [[Network2/Concept/Latency|latency]], [[Network2/Concept/Jitter|jitter]], [[Network2/Concept/Availability|availability]], [[Network2/Concept/Model|model]], [[Network2/Concept/Unicast|unicast]], [[Network/Concept/Multicast|multicast]], [[Network2/Concept/Broadcast|broadcast]], [[Network2/Concept/Network stack|network stack]]
+First, some baseline analysis:
+ Suppose we have a wireless link with capacity C.
+ Suppose we have N nodes.
+ Suppose each node n wants to maintain f(n) connections.
+ If f(n) = 1 then we could allocate up to C/N per connection.
+ If f(n) = N then we could allocate up to C/N^2 per connection.
+ Instructive values: C=30 Mbps, N=40, f(n)=N ==> 19 Kbps / conn. Conclusion: beware O(N^2) behavior.
 Several important numbers that we need to predict and to measure include bandwidth and latency figures:
@@ Line 22: / Line 32: @@
  UDP+IPv4           -- teredo
+Baseline overheads:
- Ethernet: 14+4
- IPv6: 40
+ [http://en.wikipedia.org/wiki/Ethernet#Ethernet_frames Ethernet]: 18
- ICMPv6: 4
- ICMP RA: 32
+ [http://en.wikipedia.org/wiki/IPv4#Packet_structure IPv4]: 20 + options
+ [http://en.wikipedia.org/wiki/IPv6_packet IPv6]: 40 + options
+ [http://en.wikipedia.org/wiki/ICMPv6#Packet_format ICMPv6]: 4
+ [http://tools.ietf.org/html/rfc4861#page-18 ICMPv6 RA]: 16 + prefix+{32} + mtu?{8}
+ [http://en.wikipedia.org/wiki/User_Datagram_Protocol#Packet_structure UDP]: 4
+ [http://en.wikipedia.org/wiki/Transmission_Control_Protocol#TCP_segment_structure TCP]: 20 + options?
+ [http://en.wikipedia.org/wiki/Transport_Layer_Security#TLS_record_protocol TLS]: 5 + mac?{16,20,32} + pad?{4,8,16}
+ [http://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-messages D-Bus]: 12 + type-array
+ [http://xmpp.org/extensions/xep-0045.html#message XMPP MUC]: 50 + jids

Network2/Dynamics: Difference between revisions

Latest revision as of 20:14, 29 August 2010

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